Method and device for rotating a wafer

ABSTRACT

Method and device for rotating a wafer which is arranged floating in a reactor. The wafer is treated in a reactor of this nature, and it is important for this treatment to be carried out as uniformly as possible. For this purpose, it is proposed to rotate the wafer by allowing the gas flow to emerge perpendicular to the surface of the wafer and then to impart to this gas a component which is tangential with respect to the wafer, thus generating rotation. This tangential component may be generated by the provision of grooves, which may be of spiral or circular design.

REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.09/936,257, filed Jan. 11, 2002, now U.S. Pat. No. 6,824,619, which isthe U.S. national phase of International Application No. PCT/NL00/00154,filed Mar. 8, 2000, which claims priority from Netherlands PatentApplication No. 1011487, filed Mar. 8, 1999.

FIELD OF THE INVENTION

The present invention relates to a method for rotating a disc-shapedobject, such as a wafer, wherein along a side of said object a gas flowis directed, giving a rotation to said object, wherein said gas flow isgiven the rotation generating component being tangential to said objectby a pattern of grooves.

BACKGROUND OF THE INVENTION

Such a method is known from U.S. Pat. No. 3,706,475. In thisspecification a device is disclosed for transporting wafers. The devicecomprises an elongated trajectory and from the lower side gas is addedin such a way that except from a transferring movement also a rotatingmovement is given to the wafer.

From US 393068 a method is known for rotating an object such as a waferfrom semi conducting material placed in a reactor. During the treatmentof a single wafer which is held floating in a reactor, it is importantfor a treatment of this nature to be carried out as uniformly aspossible. For this purpose, it is proposed, in the prior art, to imparta rotational movement to the wafer. This rotational movement is imposed,according to the prior art, by having the gas-introduction openingsopening out not perpendicular to the wafer surface, but rather havingthem end at an acute angle with respect to the wafer surface(“directional air jets”). As a result, a propulsive movement is impartedto the wafer.

However, drilling the gas-introduction openings in this way has provento be particularly complicated while, in addition, the rotational speedwhich can be achieved is limited, owing to the fact that the gas whichflows out very quickly loses its tangential flow component. Moreover,reactor walls of this nature are complicated to produce, since openingshave to be drilled at an angle with respect to the wall.

SUMMARY OF THE INVENTION

The object of the present invention is to avoid these drawbacks whilenevertheless maintaining the rotation of the wafer and making itpossible, in a relatively inexpensive and simple manner, to impose arotation of this nature on the wafer.

It is a further aim of the subject invention to accurately position thewafer to realise effective treatment thereof.

This aim is realised with the method as described above in that saidobject is floatingly received in a compartment being closed on allsides, said object being substantially rotating only and in that alongthe other side of said object, a further gas flow is directed.

Through the presence of a groove pattern the gas flow is given acomponent of movement extending tangentially to the wafer, i.e. gives arotating movement to the wafer. Furthermore, the wafer is subjected fromthe other side to a further gas flow, so that this is accuratelypositioned in the reactor. Also the gas flows are controlled andprovided such that the wafer substantially only rotates and does notexecute a translating movement.

According to a preferred embodiment gas flow is blown in a directionsubstantially perpendicular to said object from a gas introductionopening in the reactor.

Surprisingly, it has been found that by providing a pattern of groovesit is possible to affect the direction of flow of the gas. The gas willpreferably begin to flow in the direction of the groove, since this isthe path of least resistance. The gas flow is guided in this way overthe entire distance which the groove covers. If the direction of thegroove contains a tangential component, a tangential flow component isalso imparted to the gas. This tangential flow component imposesrotation on the wafer. Grooves of this nature can be produced relativelyeasily by milling. The pattern of grooves may have any desired shape.According to an advantageous design, the pattern of grooves is arrangedin the shape of a spiral. In this case, the grooves are preferablyarranged in such a manner that the spiral starts in the vicinity of thecentre of the wafer and ends in the vicinity of the circumferential edgethereof. The desired rotational speed can be set by means of the shapeof the spiral grooves. The total quantity of gas supplied to the wafercan therefore be selected independently of the desired rotational speedand can be set in such a manner that optimum axial and radial supportand a uniform process result can be obtained. This can be achieved byadapting the shape of the spiral grooves. As a result, it is possible towork with comparatively small quantities of gases, as is desirable inorder to maintain the uniformity inside the reactor.

This uniformity can be increased still further by also arranging theopenings from which the gases emerge in a spiral pattern. This meansthat, according to a preferred embodiment, the openings extendessentially perpendicular to the surface of the wafer, but if theseopenings are joined by an imaginary line, the result is a spiral whoseorigin preferably also lies in the vicinity of the desired centre of thewafer and whose end lies in the vicinity of the circumferential edgethereof. During rotation, a point on the wafer does not always “see” thesame openings arranged in a circle, which in the prior art causes anannular treatment pattern.

The combination of the rotation and the spiral pattern ofgas-introduction openings results in a particularly uniform distributionof the treatment gases and a particularly uniform treatment of the wafersurface.

Another possible design of the pattern of grooves consists inconstructing this pattern from one or more circle segments. In thiscase, it is important for a gas-introduction opening to be situated inthe vicinity of one of the ends of the groove. In this case too, the gasflow will preferably begin to flow in the direction of the groove. Sincethe direction of the groove is perfectly tangential, this method ofrotational driving has proven particularly effective. Another advantageof this variant is that the rotational driving is virtually independentof the axial bearing of the wafer or, in other words, of the gas flowwhich keeps the wafer floating. For example, it is possible to increaseor interrupt the gas flow for providing the rotational drive, while thegas flow for keeping the wafer floating is maintained at a constantlevel. As a result, the rotational speed of the wafer changes, while theother conditions in the reactor remain virtually unchanged. Positioningthe grooves, which are arranged as circle segments, in the vicinity ofthe edge of the wafer maximizes the drive moment and the efficiency ofthe rotational drive. Also arranging a gas-discharge opening in thevicinity of the other end of the groove further increases the efficiencyof the rotational drive. The direction of rotation is reversed byreversing the direction of flow of the gas through the rotational drivegroove.

According to a further preferred embodiment the gas flow imposingrotation to the wafer is, in the case that the wafer is in horizontalposition in the reactor, introduced at the upper side of the wafer.I.e., rotational drive can be realized both from above, from below aswell as from both sides.

The invention also relates to a reactor for the floating, rotationaltreatment of semiconductor wafers, comprising a top part and a bottompart, between which a chamber which accommodates the wafer is delimited,the said top part and bottom part being provided with gas-supplyopenings, the gas-introduction openings extending essentiallyperpendicular to the top part and/or bottom part and a pattern ofgrooves, which imparts to the said gas flow a component which istangential with respect to the said object, being arranged in at leastone of the said parts.

This reactor may be provided with the particular designs describedabove.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference toan exemplary embodiment which is illustrated in the drawing, in which:

FIG. 1 shows a diagrammatic, sectional view of a reactor which isprovided with a wafer arranged floating therein;

FIG. 2 shows a plan view of the cross section taken on line II-II fromFIG. 1;

FIG. 3 diagrammatically shows a spiral with a few important parameters,and

FIG. 4 shows a plan view of a variant of the pattern of groovesaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, a reactor is denoted overall by 1. This reactor is shown onlyin part and comprises a top part 2 and bottom part 3. In any desiredway, which is not illustrated, a wafer 10 may be accommodated in thechamber or treatment space 12 delimited between these parts 2 and 3. Thetreatment gas for the wafer is introduced via gas-introduction openings4 both above and below the wafer, and this wafer then adopts a floatingposition. Gas is discharged via discharge openings 7 which may be of anyconceivable form and emerge at a circumferential channel 6 which isconnected to a discharge line 5.

In order to impart rotation to the wafer, the top part, as can be seenfrom FIGS. 1 and 2, is provided with a number of grooves 9. Thesegrooves 9 are spiral-shaped, and the origin of the spiral lies in thevicinity of the aimed centre 11 of the wafer 10. The end of the spiralis situated in the vicinity of the circumferential edge of the wafer.Grooves 9 with the shape of a logarithmic spiral are chosen, asillustrated in FIG. 3. In this figure, the grooves are denoted by 9,while the raised part situated between the grooves, which is known asthe dam, is denoted by 15; α indicates the groove angle, γ_(groove)indicates the groove width, while γ_(dam) indicates the dam width. θrepresents the spiral angle co-ordinate. P1 is the pressure at theinternal diameter and P2 is the pressure at the external diameter. Theshape of a logarithmic spiral is described by:r(θ)=r ₁ eθ ^(tan α).

By way of example, the depth of the grooves is approximately 0.15 mm,and there are ten grooves, with a groove/dam ratio of 1:3 and a grooveangle of 42°.

It has been found that a significant fraction of gas leaving theintroduction openings 4 moves along these grooves 9 (least resistance),thus imposing rotation on the wafer.

Grooves of this nature may be formed in a subsequent stage, in contrastto the oblique drilled holes.

In order to further ensure the uniformity of the gas supply over thewafer surface, the introduction openings 4 are arranged along animaginary spiral line 8. The origin of this spiral is likewise situatedin the vicinity of the desired centre 11 of the wafer.

By varying the various parameters which determine the shape of thegroove, it is possible to control the rotational speed. Some of thesefactors include the depth of the groove, the groove angle, thegroove/darn ratio, the number of grooves, etc. This can be influencedfurther by effectively positioning the introduction openings 4 withrespect to the drive grooves 9.

Tests have shown that with a continuous flow of gas a stable rotation ofthe corresponding wafer is achieved after approximately 10 secondsstarting from an initial situation. Naturally, this too is dependent onthe conditions, and this time can be reduced considerably depending onthe requirements imposed.

It will be understood that a corresponding design can be arranged on theunderside. All this depends on the intended treatment. The speed atwhich the wafer is rotated is dependent on the process and preferablylies between 2 and 100 rpm.

FIG. 4 shows part of a variant of the invention. In this design, thereare no spiral-shaped grooves, but rather a number of circle segments 19which, in the design illustrated in FIG. 4, lie on the same circle. Inthe design illustrated in that figure, there are also gas-introductionopenings 14 and 16.

As in the preceding designs, the openings extend essentiallyperpendicular to the plane of the drawing. If gas is introduced throughopenings 14, in the design in accordance with FIG. 4 the rotation willbe to the left, while if gas is supplied from the openings 16, rotationwill be to the right. The position of the rotational drive grooves isselected to be in the vicinity of the edge of the wafer, since thismaximises the drive moment and the efficiency of the driving. Theefficiency of the rotational driving can be increased still further byinjecting gas in the vicinity of one end of the groove and discharginggas in the vicinity of the other end of the groove.

It should be understood that it is possible to use a number of circlesegments of different radii.

Moreover, it is possible to make various gas-introduction openings,optionally in combination with gas-discharge openings, which arelikewise situated in the vicinity of the circle segments. Moreover, inthe latter case, the direction of flow between gas-introduction openingand gas-discharge opening can be periodically reversed, if desired.

Moreover, it will be understood from the two variant designs shownabove, that other groove patterns are possible; all that is importantfor the invention is that the local depression caused by the groovesimparts a rotation-creating component to the gas which is blown in theperpendicular direction and may be diverted in the horizontal directionbefore the wafer.

Although the invention is described above with reference to a preferredembodiment, variants which lie within the scope of the appended claimswill immediately be obvious to people who are skilled in the art afterthey have read the above text. Although the invention is described withreference to moving a wafer in a reactor, it can equally well be usedfor moving any other object in any other type of chamber.

1. A method of semiconductor processing, comprising: loading asemiconductor wafer into a reaction chamber, at least one of the upperor lower surfaces of the chamber comprising a pattern of grooves and gasinlets, wherein the grooves define a plurality of circle segments;wherein the center of the circle is coaxial with a center of the waferand wherein each of the circle segments has provided in the circlesegment a first hole near one end of the circle segment and a secondhole arranged near the opposite end of the circle segment; floatinglysupporting the wafer inside the chamber by streaming gas directlyagainst a bottom of the wafer; rotating the floatingly supported waferby flowing gas directly against the wafer using the first hole of thecircle segment as a gas introduction hole and using the second hole ofthe circle segment as a gas exit hole; and reversing a direction of thewafer rotational driving force by using the first hole of the circlesegments as a gas exit hole and the second hole of the circle segmentsas a gas introduction hole.
 2. The method of claim 1, wherein the uppersurface comprises the pattern of grooves and gas inlets.
 3. The methodof claim 2, wherein floatingly supporting the wafer comprises streaminggas out of gas holes in the bottom surface.
 4. The method of claim 1,wherein rotating the wafer comprises varying a rotational speed of thewafer while maintaining the wafer at a constant vertical height relativeto the lower surface.
 5. The method of claim 1, wherein the gas inletsare perpendicular to the upper surface.